The invention is generally in the field of optical particle sensing and provides systems and methods for cooling optical sources used in optical particle sensors. The cooling systems of the present invention substantially increase the operating life of optical sources, such as a laser, within the sensor and are relatively inexpensive and simple to incorporate into an optical particle sensor.
Optical particle sensors and counters are useful in a variety of industrial applications where it is important that the purity of materials used in a process be continuously monitored. For example, in semi-conductor and other clean-room settings, or industries requiring sterile and pure production (e.g., pharmaceuticals), material fluids that are used to make the end product are continuously monitored to ensure adequate purity and that any unwanted particles suspended in the fluid is within an acceptable tolerance range. It is particularly advantageous to rapidly identify when a fluid is contaminated with unwanted particles so that the process can be stopped at an early stage, thereby avoiding wasteful manufacture of defective product.
The importance of particle monitoring sensors is reflected in the continuous and ongoing improvement and development of these devices to improve reliability and throughput and to enable detection and characterization of particles having smaller sizes. In particular, particle measuring devices and particle sensors are becoming more sophisticated, capable of detecting sub-micron particles at higher fluid sampling rates (e.g., 1 CFM and higher). This improvement is at least partly a result of incorporation of more powerful optical sources such as laser diodes and diode arrays capable of delivering high radiant powers to samples subject to analysis. Optical sources that illuminate samples with high radiant power also, however, generate a substantial amount of heat. Studies indicate that laser operating life doubles for about every 10° C. drop in operating temperature. Accordingly, it is vital that optical particle counters with high energy optical sources be thermally managed in a manner compatible with clean room manufacturing processes. Prolonging optical source lifetime provides cost-savings beyond simply avoiding optical source replacement. Longer optical source lifetime increases process reliability and decreases process downtime. These advantages arise by avoiding unnecessary calibration that is required when an optical source within the sensor is replaced, or the entire sensor replaced. In addition, effective cooling of optical sources in particle counters provides a more reliable light output, thereby reducing noise and enhancing detection. The thermal management and control of the present invention results in improved measuring device capabilities and reliability.
Cooling mechanisms commonly used for optical sources in particle counters include active thermoelectric cooling which often require a substantial amount of power. For example, for a particle sensor requiring 13 W of energy to deliver 1.6 W of laser power from a laser diode, about 7 W of the 13 W total is for cooling the laser to a 20° C. delta temperature (US Pat. Pub. 2006/0038998). Although sample fluid has been used to cool an aperture element associated with the optical communication between the optical source and sample within a sample chamber (U.S. Pat. Pub. 2006/0038998), flow of exhaust sample fluid has not been used to directly cool an optical source. Other strategies for controlling the temperature of optical sources in optical particle sensors includes the use of a variety of device components that are separate from the exhaust fluid, including by heat sinks, powered cooling systems (U.S. Pat. Nos. 6,690,696; 6,091,494; 5,134,622) and forced air systems (U.S. Pat. No. 5,029,335).
Another need in the art relates to particle measuring devices that are associated with certain manufacturing processes common in clean room manufacturing and high-purity settings (e.g., semi-conductor or pharmaceutical manufacture). Such clean rooms require minimum case openings to ensure that access to the measurement instrument does not constitute a significant source of contaminants to the monitored environment. In addition, minimizing case openings facilitates easier biological cleaning and room decontamination, including cleaning and decontamination of the particle sensor. Accordingly, standard cooling techniques such as enclosure fans are inappropriate for these applications. The invention addresses the need in the art for cooling mechanisms that are capable of supplying adequate cooling and are not prone to these contamination issues.
The problem of heat generation by an optical source is generally recognized (e.g., U.S. Pat. Nos. 6,091,494; 5,029,335; 6,690,696), and accordingly heat dissipating means are generally provided with such optical sources. The available solutions, however, suffer from one or more limitations of complexity, expense, undesirable additional energy requirements, or are incompatible with the particle sensors of the present invention. Although particle sensors may have some residual cooling attributed to the fact that relatively cool sample fluid flows through the sample chamber that interacts with the optical source, they suffer from the limitation of not being able to adequately cool the optical source. Accordingly, those sensors generally require an active cooling mechanism to avoid excessive optical source operating temperature.
As will be understood from the forgoing description, optical particle sensors having thermally controlled optical sources are needed, particularly optical particle sensor having cooled optical sources exhibiting enhanced operating lifetimes. An additional need is for systems for providing thermal control of these sensors that do not require substantial additional power input. Furthermore, the thermal control in these sensing systems should be readily incorporated into optical particle sensors currently in use without a need for unduly excessive additional design and expense.